How to read voltage drop from battery

[Red_MAv]

I know I have read this before but cant find it with search. I have a battery that keeps going dead after 3 days yet charges fine. The alternator is putting out 13.9 but it keeps going flat. Using a volt meter how do i check with everything turned off how much is still being drawn from the battery. I dont want to just go and buy a new battery and end up with the same problem in a week.

[pcman]

using a volt meter you cant what you need is a amps gauge

dissconect the positive terminal then hook in the amps gauge and see how much current its using with the ignition off

dont try and start the car or turn the headlights on cause you will destroy the amps gauge unless its a huge one

i just use a cheapo mutimeter than has a 0-10amps scale if its drawing more than 10 amps with the ignition off you have a MAJOR problem

[Red_MAv]

thanks PCMAN, Multimeter was the word I was looking for and is what I will be using.

[Pinball]

or optionally see if you can beg/borrow/scrounge a hall effect clamp meter. It may be that you're drawing more sultanas than your alternator can provide.

Also, once charged, take the battery down to local auto sparky/battery world/supercheap and ask to get it load tested. Voltage can be fine on the meter noload, but start pulling from it and you may find that all you are reading is a surface charge.

Spock

[Red_MAv]

OK When i hook it up and open the door the light comes on and it reads 2.8 amps so i know its all connected ok. Close the door and it drops to .12 amps.
Is this too much draw? The car is a Ford Telstar and the battery isnt huge. I cant see any amp hours written on the battery just CCA's so cant calculate how long it would take to flatten the thing although I know its about 2 and a half days at present.

[joel HJ60]

Allowable draw is .02amps (correct me if im wrong) Joel

[bazooked]

.o5 is max and .o7 for the later model falcons, .12 is to much, could be ur imobiliser if ya got 1 fitted as they tend to do strange things after a while.

[Red_MAv]

Yep, got one of them fitted, maybe its a visit to the auto elecs to sort it all out.

[drivesafe]

Hi Red_MAv, many moons ago, I use to fit car alarms.

If anything went wrong with the car after we fitted the alarm, we got the blame.

One of the most common cause of problems was the boot light staying on. Someone would put items in the boot and bump the switch and as it was now out of alinement, it stayed on, have you checked yours because the load is about that of an 18 watt globe.

Just a suggestion, cheers.

[drivesafe]

By the way, your glove box is another place to check.

Cheers.

[drivesafe]

Sorry Red_MAv, I just read your last post again and I realised you post ed .12 and not 1.2 amps, please disregard the above but that current draw is about what a relay would pull. It might pay to see if a relay is sticking.

Cheers and sorry again about the miss information

[Red_MAv]

No problems. I suspect it may be the immobiliser / central unlocking sticking maybe if that can cause it. I had one fitted about 3 years ago and it regularly stopped working with the central locking. I had to take the dash apart and find this group of 2 or 3 relays that were put in when the immobiliser went in and give them a wiggle, it usually sprang back to life. It stopped again a few months ago and I havent been bothered to do that again so maybe if thats stuck, because the central locking isnt working remotely at the moment then maybe its related.

[carts]

0.12A is bugger all. This could be an accumulation of immobiliser, stereo, clock, etc etc...

Having that load connected to a battery for 100 hours (over 3 days) is roughly equivalent to leaving your low beam headlights on for an hour. (2 55 watt beams and parkers). It should not flatten your battery in 3 days.

I would be suggesting that your battery is faulty and not holding its charge. I had a similar problem to this in my cruiser. Battery would start, run and charge fine. If i left it for a few days, the car would be a lot harder to start. I changed the battery, and now i can leave the vehicle for over 2 weeks without any dramas.

I would imagine your battery would be at least a 50Ah battery. All things considered, if the battery was in good nick, it should be capable of starting the car at least 7-10 days on from the last time it was run.

[blkmav]

Had the same problem with the mav. Fitted a new battery, now it has heaps of grunt to start if I have not driven it for a week. All I need to do now is fix the starter motor

[Red_MAv]

OK, thats it I'll buy a new battery on the weekend and see how that goes. The battery is a couple of years old anyway but I was concerned that was not the problem as it appears to charge ok. Battery will be cheaper than Autoelectrician. Thanks all for advice.

[drivesafe]

Hi Red_MAv, before you do anything, after your next drive, if you are not going to use you vehicle for a while, when you stop, remove the negative lead from your battery. For safety reasons, leave the positive lead connected.

If your battery is still going flat then it would be pretty safe to say your battery is stuffed.

If it doesn’t then you need to find the discharge.

It’s true that a small discharge of 120 ma would take a long time to flatten a fully charged battery but if your battery is not getting a good enough charge in the first place, even a small discharge of 120 ma could flatten the battery in a relatively short time.

Cheers.

[bazooked]

dont forget that the drain on ur battery is relative to the voltage in ur battery, so if its reading 9 volts ur drain in reality will be alot higher, and having a drain on ur battery constantly will reduce the life of it.

[Davidh]

Typically in a climate such as Melbourne, your battery is expected to last 2-3 years, a few more if it's a good one.
I replaced my battery last May and after 6-7 weeks it still starts first go.

It all depends on how often it's used, how long you drive for, how much load is used etc.